1. ZG (Started late, had loads of fun there, mostly due to those i raided with ofc)
2. Sunwell. (Just the whole island in itself gave the place its unique aura )
3. Ulduar (As much as its because of some awesome fights and scenaries, its for the lack of a better one)
4. Firelands (For the lack of a better raid, Ragnaros HC was pure awesomeness, eventhough we did it rather late in Cata)
5. N/A (Too early, sure we got the last tier now, but haven't farmed it yet, so too early)

1. Vanilla: Blackwing Lair
2. Burning Crusade: Karazhan
3. Wrath of the Lich King: Naxxramas (yeah, did a bit of Naxx in vanilla so wanted to clear it for once, awesome raid, probably the best ever made)
4: Cataclysm: No idea, haven't done any of the raids. (If I were to guess, probably either Blackwing Descent or Firelands)
5. Mists of Pandaria: Done everything except Siege, don't really like any of them though.

1. Why so many say Molten core? Because it's the only instance you could enter?? Bosses there are horrible, same textures, lame fights, all red... It was fine for first 40 man raid, but best? hell no... My fav is AQ40, brought up some very interesting fights.
2. Black Temple. Tough choice, so many good raids in tbc.
3. Ulduar I guess, though it's OVERRATED.
4. Firelands.
5. Siege